1. Field of the Invention
The present invention relates to a gas chromatograph used for measuring component concentrations in various samples.
2. Description of the Related Art
A gas chromatograph is provided with a column for separating sample components, a carrier gas supply unit for supplying carrier gas to the column and a detector for detecting eluted components from the column, and also has an injector for injecting a sample into the carrier gas, which is placed on the upstream side of the column.
A flow controller unit for controlling a flow rate, which includes a valve and a flow-rate sensor, is installed in the carrier gas supply unit so that a carrier gas, supplied from a carrier gas inlet, is supplied to a column from the valve through the flow-rate sensor.
With respect to the carrier gas supply unit, a structure in which a carrier gas passage is formed inside a metal substrate has been proposed (see Japanese Patent Application Laid-Open No. 11-218528). In this metal substrate, only one carrier gas passage is formed.
In the case of using a packed column in which a filler has been filled up as the column, since a bleeding component from the packed column is large, upon a temperature-rise analysis (that is, a method in which the temperature of the packed column raises during analysis), a base line on the chromatogram fluctuates largely, affecting adversely on a quantitative analysis. For this reason, generally, two of the same packed columns are installed, and these are connected to respective detectors. Then, the fluctuations in the base line are cancelled by obtaining a difference between detection outputs of these detectors.
The carrier gas has been supplied to each of the packed columns from each of the corresponding carrier gas supply units.
However, generally, a gas chromatograph has a column oven having a temperature ranging from room temperature to about 400° C. and a sample vaporization chamber having a temperature of about 250° C., together with heat-generating parts, such as a detector. Hence, there is a temperature difference of 2 to 3° C. between the carrier gas passages of the two carrier gas supply units.
It has generally been known that, even if the volume flow rate of gas is constant, there is a change of 0.6% in the mass flow rate when the surrounding temperature changes by 1° C. Moreover, the temperature coefficient of the flow-rate sensor is about 0.4%/° C. For this reason, a difference in a level of 2 to 3% occurs between the carrier-gas flow rates of the two carrier gas passages due to the above-mentioned temperature difference of 2 to 3° C. Consequently, base-line fluctuations occur in the chromatogram, resulting in adverse effect on the quantitative analysis.
There are differences among the flow rates of carrier gases, supplied from carrier gas passages made of a plurality of flow-passage assemblies to supply gases to a plurality of packed columns due to the above-mentioned temperature difference in the passage assemblies, resulting in a base-line shift of chromatogram that affects adversely on the quantitative analysis.
There have been demands for a constant carrier-gas flow rate not only in an attempt to cancel base-line fluctuations by obtaining a difference between a pair of detectors, but also in an attempt to use a plurality of gas chromatographs under the same conditions.
Moreover, there have been the same demands in capillary columns as in packed columns.